Renaissance of Topotactic Ion-Exchange for Functional Solids with Close Packed Structures

Recently, many new, complex, functional oxides have been discovered with the surprising use of topotactic ion-exchange reactions on close-packed structures, such as found for wurtzite, rutile, perovskite, and other structure types. Despite a lack of apparent cation-diffusion pathways in these structure types, synthetic low-temperature transformations are possible with the interdiffusion and exchange of functional cations possessing ns² stereoactive lone pairs (e. g., Sn(II)) or unpaired nd^x electrons (e. g., Co(II)), targeting new and favorable modulations of their electronic, magnetic, or catalytic properties. This enables a synergistic blending of new functionality to an underlying three-dimensional connectivity, i. e., [-M−O-M-O-]_n, that is maintained during the transformation. In many cases, this tactic represents the only known pathway to prepare thermodynamically unstable solids that otherwise would commonly decompose by phase segregation, such as that recently applied to the discovery of many new small bandgap semiconductors.     

Cryogenic OrbiSIMS Localizes Semi-Volatile Molecules in Biological Tissues

OrbiSIMS is a recently developed instrument for label-free imaging of chemicals with micron spatial resolution and high mass resolution. We report a cryogenic workflow for OrbiSIMS (Cryo-OrbiSIMS) that improves chemical detection of lipids and other biomolecules in tissues. Cryo-OrbiSIMS boosts ionization yield and decreases ion-beam induced fragmentation, greatly improving the detection of biomolecules such as triacylglycerides. It also increases chemical coverage to include molecules with intermediate or high vapor pressures, such as free fatty acids and semi-volatile organic compounds (SVOCs). We find that Cryo-OrbiSIMS reveals the hitherto unknown localization patterns of SVOCs with high spatial and chemical resolution in diverse plant, animal, and human tissues. We also show that Cryo-OrbiSIMS can be combined with genetic analysis to identify enzymes regulating SVOC metabolism. Cryo-OrbiSIMS is applicable to high resolution imaging of a wide variety of non-volatile and semi-volatile molecules across many areas of biomedicine.     

Dynamic Scattering and Material Flow in a Nematic Liquid Crystal

Results are presented which show how defects in a nematic liquid crystal can be used to investigate material flow when external electric fields are applied. These results include measurements of the size of flow cells, which were created between the electrodes by an electric field. The electrodes, which were made of transparent conductive coated glass, were placed in a vertical position so that flow cells could be observed from the top while dynamic scattering was observed when viewing normal to the electrodes.     

Enhanced wet adhesion and shear of elastomeric micro-fiber arrays with mushroom tip geometry and a photopolymerized p(DMA-co-MEA) tip coating

Using principles inspired by the study of naturally occurring sticky systems such as the micro- and nanoscale fibers on the toes of geckos and the adhesive proteins secreted by marine animals such as mussels, this study describes the development and evaluation of a novel patterned and coated elastomeric microfibrillar material for enhanced repeatable adhesion and shear in wet environments. A multistep fabrication process consisting of optical lithography, micromolding, polymer synthesis, dipping, stamping, and photopolymerization is described to produce uniform arrays of polyurethane elastomeric microfibers with mushroom-shaped tips coated with a thin layer of lightly cross-linked p(DMA-co-MEA), an intrinsically adhesive synthetic polymer. Adhesion and shear force characterization of these arrays in contact with a glass hemisphere is demonstrated, and significant pull-off force, overall work of adhesion, and shear force enhancements in submerged aqueous environments are shown when compared to both unpatterned and uncoated samples, as well as previously evaluated patterned and coated arrays with differing geometry. Such materials may have potential value as repeatable adhesives for wet environments, such as for medical devices.     

How universal are Fibonacci patterns?

Pattern patterns, or phyllotaxis, the arrangements of phylla (flowers, leaves, bracts, florets) in the neighborhood of growth tips, have intrigued natural scientists for over four hundred years. Prominent amongst the observed features is the fact that phylla lie on families of alternately oriented spirals and that the numbers in these families belong to subsets  {m _j } of the integers defined by the Fibonacci rule m _j + 1 = m _j  + m _j − 1. The corresponding patterns, which we call Fibonacci patterns, are widespread and universal on plants. Our goal in this paper is to ask if they may also be seen in other physical structures and to try to quantify the circumstances under which one may expect Fibonacci patterns to occur.     

Students' Attitudes Toward Science as Predictors of Gains on Student Content Knowledge: Benefits of an After‐School Program

High‐quality after‐school programs devoted to science have the potential to enhance students' science knowledge and attitudes, which may impact their decisions about pursuing science‐related careers. Because of the unique nature of these informal learning environments, an understanding of the relationships among aspects of students' content knowledge acquisition and attitudes toward science may aid in the development of effective science‐related interventions. We investigated the impact of a semester‐long after‐school intervention utilizing an inquiry‐based infectious diseases curriculum (designed for use after‐school) on 63 urban students' content knowledge and aspects of their attitudes toward science. Content knowledge increased 24.6% from pretest to posttest. Multiple regression analyses indicated suggested that the “self‐directed effort” subscale of the Simpson–Troost Attitude Questionnaire—Revised best predicted increases in students' science content knowledge. The construct “science is fun for me” served as a suppressor effect. These findings suggest that future after‐school programs focusing on aspects of attitudes toward science most closely associated with gains in content knowledge might improve students' enthusiasm and academic preparedness for additional science coursework by improving student attitudes toward their perceptions of their self‐directed effort.